Over the past several years this ongoing filariasis research program has been examining the immune response in outbred and inbred Mongolian jirds (Meriones unguiculatus) infected with the lymphatic-dwelling filarial worm, Brugia pahangi. Further work in this area will continue using immune-deficient mice (thymus-deficient nude, and sex-linked B-cell-defective CBA/N strains) as murine models to study relevant effector mechanisms in chronic filarial infections. The use of immunologically well defined rodent hosts has distinct advantages that are superior to use of the immunologically less well defined Mongolian jird. There will be completion of studies in inbred jirds on circulating immune complexes present in infected animals and their role in short- and long-term infections. Further work will be carried out on Wuchereria bancrofti infections in monkey hosts as animals with mirofilaremias become available.